linux-kernel - Re: [PATCH v4 9/9] cxl/mem: Add payload dumping for debug

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Message-ID: <CAPcyv4j+DZq7fkRTW+_O1-AtAQwOPD65A8M5AWg7XU9N+TksRA@mail.gmail.com>
Date:   Tue, 16 Feb 2021 08:48:32 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     Ben Widawsky <ben.widawsky@...el.com>, linux-cxl@...r.kernel.org,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Chris Browy <cbrowy@...ry-design.com>,
        Christoph Hellwig <hch@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Jon Masters <jcm@...masters.org>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        "John Groves (jgroves)" <jgroves@...ron.com>,
        "Kelley, Sean V" <sean.v.kelley@...el.com>
Subject: Re: [PATCH v4 9/9] cxl/mem: Add payload dumping for debug

On Tue, Feb 16, 2021 at 7:50 AM Jonathan Cameron
<Jonathan.Cameron@...wei.com> wrote:
>
> On Mon, 15 Feb 2021 17:45:38 -0800
> Ben Widawsky <ben.widawsky@...el.com> wrote:
>
> > It's often useful in debug scenarios to see what the hardware has dumped
> > out. As it stands today, any device error will result in the payload not
> > being copied out, so there is no way to triage commands which weren't
> > expected to fail (and sometimes the payload may have that information).
> >
> > The functionality is protected by normal kernel security mechanisms as
> > well as a CONFIG option in the CXL driver.
> >
> > This was extracted from the original version of the CXL enabling patch
> > series.
> >
> > Signed-off-by: Ben Widawsky <ben.widawsky@...el.com>
>
> My gut feeling here is use a tracepoint rather than spamming the kernel
> log.  Alternatively just don't bother merging this patch - it's on the list
> now anyway so trivial for anyone doing such debug to pick it up.
>

I've long wanted to make dev_dbg() a way to declare trace-points. With
that, enabling it as a log message, or a trace-point is user policy.
The value of this is having it readily available, not digging up a
patch off the list for a debug session.